Field of the Invention
The invention relates to a method of producing a contact element having a base body made of a material with a good electrical conductivity (first material) and a contact layer made of a material with a less good electrical conductivity which is resistant to arc erosion (second material), which includes impregnating a sinter structure of the contact layer with the material of the base body. The invention also relates to a device for carrying out the method, wherein a cup-like mold is formed of metal, preferably of steel or stainless steel or a mold is formed at least partially from ceramic.
Contact elements which have to conduct an arc during a switching operation must satisfy various conditions. Firstly, the contact element must have a sufficiently high electrical conductivity when the switch is closed. Secondly, the contact element must not erode too quickly when a switching arc is formed, so that the service life of the switchgear remains sufficiently high. While it is possible, in the case of gas-insulated high-voltage circuit breakers to divide the contact configuration into contact elements which conduct the rated current and contact elements which conduct the arc and accordingly have to be resistant to erosion, in the case of a vacuum circuit breaker it is not possible to provide any contact elements which conduct the rated current, so that the single contact-element configuration must conduct both the rated current as well as the arc.
In the event of a switching-off operation in a vacuum chamber, at certain current intensities a so-called contracted arc is formed, which is set in rotation by suitable shaping of the contact elements, so that the erosion of the contact material can be kept at a low level. Nevertheless, it is necessary to provide the surface of the opposite contact elements with erosion-resistant material, so that the erosion of the contact elements, as mentioned at the outset, remains low.
In the past, the contact elements for a vacuum circuit breaker have been made from two or more metallic components, in such a way that a sintered metal structure, which often is formed essentially of chromium, is impregnated with copper, so that a contact body made of a chromium-copper alloy is formed. On an industrial scale, such chromium-copper contacts may as a rule also be produced by sintering from a powder mixture of the corresponding metals, with contact elements in this case being formed which are made completely of this mixture.
Since the erosion-resistant material, for example chromium, has a lower electrical conductivity than copper, it has been sought to keep the chromium content in the complete contact element as low as possible, which has been accomplished in a very wide variety of ways. For example, a contact plate made of the composite metal may be applied to a base body. It is known, for example, from German Published, Non-Prosecuted Patent Application DE 31 07 688 A1 to coat the surface by a plasma spraying process.
German Published, Non-Prosecuted Patent Application DE 35 41 584 A1 has disclosed a method and a device for producing metal-composite materials and contact elements produced from those materials for electrical switchgear. In the case of those contact elements the surface of the base body is fused in some regions by using a suitable energy beam and pulverulent active components are fed to the volume of the melt and are incorporated into the base material.
In the method according to European Patent 0 458 922 B1, corresponding to U.S. Pat. No. 5,254,185, the substrate surface, that is to say the surface of the support body, is fused locally and the additional material is applied in the form of a loose powder layer to the substrate surface. As a result, the powder situated in the powder layer is wetted or the powder layer is impregnated with the liquid material from the fused local region, so that the powder of the powder layer is bound into the surface of the substrate and the desired surface layer is formed.